Duridium was a type of ore. (DS9 episodes: "The Adversary", "Blaze of Glory")

Duridium was mined at the Gallitep labor camp on Bajor during the Cardassian Occupation. (DS9 - Terok Nor novel: Night of the Wolves)

Duridium was also mined on the Hupyrian homeworld. Grand Nagus Oblat owned a duridium mine on that planet. (DS9 reference: Legends of the Ferengi)